Strange thing for a US congressman to have been claiming. Especially since, according to reports, Fifty Shades of Grey isn't even in the prison library at Guantanamo.

Guantanamo Fifty Shades of Grey claim denied by lawyer
BBC News
A lawyer for a detainee at Guantanamo Bay's highest-security section has rubbished reports that Fifty Shades of Grey is a favourite read among inmates. A US congressman made the claim last month after visiting Camp 7, saying it showed the inmates were "not exactly holy warriors".
Lawyer James Connell says guards this week gave a copy of the erotic novel to his client, possibly as a joke. But 9/11 accused Ammar al-Baluchi had no interest in the book, he said.